This is a proposal to develop a method for measuring oxygen-uptake and respiratory-quotient of sick patients. The method is based on proportional sampling of airway flow and has the particular advantage that it can easily be carried out on patients with lung disease receiving respirator support, with minimal bulk of apparatus, without change or modification of the respirator, and without changing the respiratory gases being administered. The method is easily adaptable to automation, and is free of many of the errors of previous methods. The technology on which this development is based also suggests the feasibility of the development of a flow-meter for measuring respiratory (airway) gas flow which will inherently eliminate errors due to the density or temperature of the gas measured, because it is based on "stream splitting" and the volumetric measurment of a small but constant sample of the total flow.